Sandbox with Fold-Out Seats

Join the sides into a square, short sides inset between the long sides. Pocket holes or pre-drilled 1-1/4" screws through the long sides — either is fine on a box this size.

Check the diagonals match before moving on; the folding panels are rectangles, and they only close cleanly over a rectangular box.

Screw two planks to the box top on each side — these are the only planks that don't move. Countersink the screws through the top and keep the 1/2" gap between planks; that spacing continues across the whole folding surface.

Screw two planks (1/2" apart) across each pair of 2x4 armrests. Inset the 2x4s AT LEAST 1" from the plank ends — that inset is what lets the assembly fold down into the box without jamming.

Build two.

Attach the first set of hinges to each seat panel on the side OPPOSITE the armrests, then attach that hinged edge to the fixed planks on the box. (Easier in that order — the source builder learned it the fumbling way.) Keep the 1/2" gap at the hinge line; it's the clearance the fold pivots through.

Same construction as the seats: two planks, 1/2" apart, screwed across the 12-1/2" back support 2x4s. The longer 2x4s do double duty — they're the backrest structure when open and the lift handles when closed.

Attach the second set of hinges to each backrest on the side opposite its 2x4s, then hinge it to the seat panel — easiest with the seat folded up. Same 1/2" gap.

Now cycle it: closed lid → fold once to seat → fold again to backrest, both sides. It should move without force. Add the gate handles, sand every edge and corner like it's a toy (it is), check the folds for pinch points, and fill with sand — on landscape fabric, so the box drains.